In general, a semiconductor fabrication apparatus may generate plasma during dry etching of a semiconductor structure. The plasma may be generated by a physical and/or chemical reaction of a reactant gas with the semiconductor structure in a process chamber of the semiconductor fabrication apparatus. The plasma may be exposed at specific frequencies from the process chamber of the semiconductor fabrication apparatus during the dry etching of the semiconductor structure. Process environments of the process chamber, a process-change point of a semiconductor fabrication process, or the shape of the semiconductor structure may be explained based on the specific frequencies of the plasma. Accordingly, the plasma can be captured from the process chamber during the dry etching of the semiconductor structure and used to predict the shape of the semiconductor structure.